This video shows what we saw at Lango Camp.
…mtDNA represents just a single locus in the genome and need not represent the true species phylogeny since a single gene tree can differ from the consensus species tree of the taxa in question. Generalizing about species relationships based on mtDNA alone is especially problematic for the Elephantidae because their core social groups (‘‘herds’’) are matrilocal, with females rarely, if ever, dispersing across groups. This results in mtDNA genealogies in both African and Asian elephants that exhibit deeper divergence and/or different phylogeographic patterns than the nuclear genome.Further strengthening of the case for two species in Africa came from work comparing these two elephants with the Asian Elephant and the relatively recently extinct Woolly Mammoth and American Mastodon. Rohland et al. (2010) reported (with my emphasis in bold characters):
We have used a combination of modern DNA sequencing and targeted PCR amplification to obtain a large data set for comparing American mastodon, woolly mammoth, Asian elephant, African savanna elephant, and African forest elephant. We unequivocally establish that the Asian elephant is the sister species to the woolly mammoth. A surprising finding from our study is that the divergence of African savanna and forest elephants—which some have argued to be two populations of the same species—is about as ancient as the divergence of Asian elephants and mammoths. Given their ancient divergence, we conclude that African savanna and forest elephants should be classified as two distinct species.
Our study also infers a strikingly deep population divergence time between forest and savanna elephant, supporting morphological and genetic studies that have classified forest and savanna elephants as distinct species. The finding of deep nuclear divergence is important in light of findings from mtDNA, which indicate that the F-haplogroup is shared between some forest and savanna elephants, implying a common maternal ancestor within the last half million years. The incongruent patterns between the nuclear genome and mtDNA (‘‘cytonuclear dissociation’’) have been hypothesized to be related to the matrilocal behavior of elephantids, whereby males disperse from core social groups (‘‘herds’’) but females do not. If forest elephant female herds experienced repeated waves of migration from dominant savanna bulls, displacing more and more of the nuclear gene pool in each wave, this could explain why today there are some savanna herds that have mtDNA that is characteristic of forest elephants but little or no trace of forest DNA in the nuclear genome. In the future, it may be possible to distinguish between models of a single ancient population split between forest and savanna elephants, or an even older split with longer drawn out gene flow, by applying methods like Isolation and Migration (IM) models to data sets including more individuals.
The problems inherent in using mitochondrial DNA have been stressed recently by Jerry Coyne in his blog, Why Evolution is True, in relation to the evolution of the Brown Bear and the Polar Bear in which conclusions drawn from mitochondrial DNA have been shown to confuse rather than illuminate. This is a screen grab from his blog:
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“Mitochondrial essentialism” and the conservation of Africa's elephantsGiven that mtDNA haplotypes among elephants are an unreliable indicator of overall genetic similarity it is unfortunate that mtDNA alone continues to be used as a guide to elephant genealogical affinities. This “mitochondrial essentialism,” the continuing use of mtDNA to partition populations and species, among elephants where morphological and nuclear markers have established that mtDNA patterns may be inaccurate or misleading, might lead to adverse results for elephant conservation, as the following examples illustrate: If mtDNA data were used as the sole basis for elephant taxonomy and population structure, elephants in the Guinean forest block could be recommended for translocation to the deserts of Mali, on the grounds that their mtDNA similarity implies that they must be genetically similar. Likewise, relying on mtDNA to infer population structure would mean that savanna elephants from Tanzania could be moved west into the Congolian tropical forest, since forest and savanna elephants in these regions share similar F clade mtDNAs. Either of these translocations would be inappropriate, since even while carrying mtDNA from the same haplogroup, individuals in forest and savanna locations are very different in nuclear genotypes, belong to different species, and are thus unlikely to thrive when moved to the wrong habitats. Although the examples are extreme, it may be equally troublesome that mtDNA-based misinterpretations of African elephant taxonomy constitute an unacknowledged potential hindrance to their proper conservation by convincing conservation groups to “continue to treat African elephants as a single species”.Although studies based solely on mitochondrial DNA appear to be useless in this and many other cases, there is a bonus as Roca and his colleagues have both pointed out and actually worked on: the use of both nuclear and mitochondrial genetic markers can more accurately determine the geographical source of poached ivory.